The Black Death 1300s - 1400s, with further outbreaks into the 1700s.
The Black Death is the name commonly given to the epidemic outbreaks of bubonic plague that killed nearly a third of the population of Europe—as many as 34 million people. It is said to have killed similar numbers in China and India. The Middle East also was hit hard. Although no totals are known, a 1348 - 1349 outbreak may have killed 400,000 in Syria. Similar numbers for Africa are reasonable.
So, the total worldwide almost certainly reaches close to 100 million.The reason this is not considered the worst, however, is that the Black Death killed those 100 million over a period of 200 years. The Great Influenza killed that number in six months.
The Black Death is traditionally attributed to one of the three forms of the plague caused by the bacterium Y.pestis (bubonic, pneumonic and septicemic). Some modern researchers, however, think it may have been caused by an Ebola like virus, or anthrax.